Various abbreviations are used, including Sqn Ldr ,Sqn. Ldr., SQNLDR and S/L in the various Air Forces of the world.
The equivalent rank in the Women's Auxiliary Air Force (WAAF), Women's Royal Air Force (WRAF) (until 1968) and Princess Mary's Royal Air Force Nursing Service (PMRAFNS) (until 1980) was Squadron Officer.
On 1 April 1918, the newly created RAF adopted its officer rank titles from the British Army, with Royal Naval Air Service Lieutenant-Commanders and Royal Flying Corps Majors becoming Majors in the RAF. In response to the proposal that the RAF should use its own rank titles, it was suggested that the RAF might use the Royal Navy's officer ranks, with the word "Air" inserted before the naval rank title. For example, the rank that later became Squadron Leader would have been Air Lieutenant-Commander. However, the Admiralty objected to this modification of their rank titles. The rank title Squadron Leader was chosen as Squadrons were typically led by RAF Majors and the term Squadron Commander had been used in the Royal Naval Air Service. The rank of Squadron Leader has been used continuously since 1 August 1919.
The rank insignia consists of a thin blue band on a slightly wider black band between two narrow blue bands on slightly wider black bands. This is worn on both the lower sleeves of the tunic or on the shoulders of the flying suit or the casual uniform.
Squadron Leaders are the lowest ranking officers that may fly a command flag. The flag may be depicted on the officer's aircraft or, should the squadron leader be in command, the flag may be flown from a flagpole or displayed on an official car as a car flag. If the Squadron Leader is in command of a numbered squadron, then the number of the squadron would also be shown on the flag.
The Royal Canadian Air Force (RCAF) used the rank until the unification of the Canadian Forces in 1968, when army-type rank titles were adopted. Canadian squadron leaders were retitled as majors. In official French Canadian usage, a squadron leader's rank title was commandant d'aviation.
The rank has been borrowed in science fiction including the Star Wars films and its extended universe of literature and comics, though (at least in the Star Wars franchise) more often as the title andor callsign of the leader of a starfighter squadron, irrespective of rank (similar to the aforementioned RAC usage; see Flight Leader), and usually with the word "Squadron" replaced by the name of the squadron, e.g. Red Leader for the commander of Red Squadron, and infrequently as an actual rank. For the most part, this is just another example of common depiction of starfighter forces in most works featuring such craft as closely paralleling contemporary (at the time the work in question was produced) real-world air forces in almost all aspects.